This invention relates generally to gas turbine engine turbines and more particularly to fairings for stationary structural members of such engines.
Gas turbine engines frequently include a stationary turbine frame, also referred to as an inter-turbine frame or turbine center frame (“TCF”), which provides a structural load path from bearings which support the rotating shafts of the engine to an outer casing, which forms a backbone structure of the engine. Turbine frames commonly include an annular, centrally-located hub surrounded by an annular outer ring, which are interconnected by a plurality of radially-extending struts. The turbine frame crosses the combustion gas flowpath of the turbine and is thus exposed to high temperatures in operation. Such frames are often referred to as “hot frames”, in contrast to other structural members which are not exposed to the combustion gas flowpath.
To protect them from high temperatures, turbine frames are typically lined with high temperature resistant materials that isolate the frame structure from hot flow path gasses. The liner must provide total flow path coverage including the frame outer ring or case, hub structure, and struts.
One known configuration to protect the struts is an interlocking split fairing arrangement in which forward and aft sections of individual fairing/nozzle components are sandwiched around the struts. This arrangement uses a tab-and-buckle (or post-and-buckle) coupling assembly having a buckle with a rectangular opening that receives generally rectangular tabs to keep the fairing halves together after assembly to the frame. An example of this tab-and-buckle arrangement is described in U.S. Pat. No. 8,152,451 to Manteiga et al.
While effective to secure the fairing halves together, the prior art rectangular post/buckle configuration, however, requires tight tolerance match machining of the post and buckle to ensure alignment and fit of the members and relies on clearance gaps in the buckle joint to accommodate assembly. This can lead to gaps at assembly and in operation, creating potential “forward facing steps” and air leakage into the flowpath.
Accordingly, there is a need for a post-and-buckle joint for a turbine strut fairing which is self-aligning.